1. Technical Field
The present invention relates to a composition of alginate gels and a method for use thereof for flow profile modification in subterranean hydrocarbon reservoirs.
2. Description of the Related Art
A commonly encountered problem in producing hydrocarbons from a subterranean reservoir is that injected or produced fluids flow preferentially through some portions of the reservoir and bypass other portions. Flow profile modification is a method by which the flow of fluids from one portion or portions of the reservoir is diverted to another portion or portions. One approach to flow profile modification in hydrocarbon reservoirs has been to fill the pore spaces in the more permeable zones with a gelled material. However, it is necessary to control the properties of the gel. Injecting the different components of a gelable composition either sequentially or simultaneously into the formation may result in incomplete mixing of the components and little or no gelation. Yet, if the components are mixed at the surface and gel substantially prior to injection, the material can't be pumped easily. Thus, it is desirable to formulate a composition with a controllable rate of gelation which allows formulation at the surface, subsequent pumping into one or more wells in communication with the reservoir, and gelation after injection into the reservoir.
Synthetic polymer gels have been used extensively for flow profile modification in hydrocarbon reservoirs. The rate and extent of gelation of polyacrylamide gels are controllable if multivalent heavy metal cations are used to crosslink carboxyl groups of the polymer chains. Cr(III) is a particularly desirable crosslinking agent. However, chromium is increasingly subject to environmental regulations.
Polysaccharide gels formed with naturally occurring biopolymers are an alternative to gels formed with synthetic polymers. Polysaccharides are environmentally innocuous; in many cases, they have been approved for use as food additives. The breakdown products of these gels are sugars, some of which are easily digested by microbes. Many polysaccharide gels are subject to direct microbial attack and, therefore, pose problems for long-term use. Polysaccharide gels also tend to undergo syneresis, or loss of fluid, upon standing.
Accordingly, it is an object of the present invention to provide a gel composition for flow profile modification in hydrocarbon reservoirs which is not subject to environmental regulations, has controllable gelation properties, is not subject to microbial attack, and undergoes minimal syneresis. It is a further object of the present invention to provide a composition that does not react unfavorably with fluids present in the oilfield environment.